Previous studies indicate hyperthermia increases the response of radioresistant tumors to ionizing radiation to a sufficient level such that they can be controlled. The objective of this research is to develop techniques combining thermal and ionizing radiation to provide greater enhancement of tumor cure. Judicious combinations of temperature variations and irradiation may permit cures of tumors which appear to be relatively radioresistant and improved cure rates of tumors which are now considered radiocurable. Tumor, normal tissue and cultured cells will be irradiated during hyperthermia treatment at variable temperatures. Fractionation studies of radiation alone and in combination with hyperthermia will be carried out to determine time-dose relationships of hyperthermia and ionizing radiation. Evaluations will be based on x-radiation doses required to cure 50% of third generation transplants of a C3H mouse mammary adenocarcinoma. Evaluations of skin response of treated mice will be done. In vitro experiments will be done with Chinese hamster ovary cells, and C3H mouse tumor cells.